Economizer

ABSTRACT

Disclosed is an economizer including a plurality of coil stacks. Each coil stack includes a tube coiled such that adjacent layers of the tube contact one another in a radial direction. Further, the coil stacks are axially spaced from one another to allow exhaust to flow between adjacent coil stacks.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/552,143 filed 27 Oct. 2011, the entirety of which is herein incorporated by reference.

BACKGROUND

Economizers are typically employed to heat a working fluid, such as water, making use of exhaust from a boiler, for example. While the exhaust may not be hot enough to be used in the boiler itself, heat from the exhaust may be recovered by the fluid carried by the economizer to improve the boiler's efficiency. In other words, the economizer is used to preheat the fluid carried therein with the exhaust heat that would otherwise have been wasted.

Some known economizers include coils and fins to increase heat transfer between the exhaust and the coils. Economizers are also known to include fans, or blowers, to force the exhaust from the boiler through the economizer.

SUMMARY

Disclosed is an economizer including a plurality of coil stacks. Each coil stack includes a tube coiled such that adjacent layers of the tube contact one another in a radial direction. Further, the coil stacks are axially spaced from one another to allow exhaust to flow between adjacent coil stacks.

These and other features of the present disclosure can be best understood from the following drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings can be briefly described as follows:

FIG. 1 is a perspective view illustrating an example economizer;

FIG. 2 illustrates a coil stack;

FIG. 3 is a schematic-type view illustrating the arrangement of adjacent coil stacks;

FIG. 4 is a cross-sectional view of a tube used to form a coil stack;

FIG. 5 includes various views of the exemplary economizer, as well as the manifolds used therein;

FIG. 6-7 show various arrangements of an economizer relative to a boiler;

FIGS. 8-10 show various views of an example economizer housing.

DETAILED DESCRIPTION

With reference to the drawings, an example economizer 10 includes a plurality of coil stacks 12 arranged relative to an inlet manifold 14 and an outlet manifold 16 (the manifolds are shown in detail in FIG. 5). The coil stacks 12 are further arranged radially about an axis A_(x) of a main exhaust flow conduit 18. The conduit 18 may optionally include a plurality of fins T disposed therein to create a circular movement of the exhaust E as it enters the economizer 10. As will be appreciated from the below, the disclosed economizer 10 provides, among other features, for efficient recovery of latent heat.

In the example, the individual coil stacks 12 are formed by wrapping a single stainless steel tube 20 about itself. For example, in FIG. 2 the coil stack 12 a was formed by wrapping the single tube 20 about the axis A_(x) such that the individual tube layers 22 a-22 i contact one another in the radial direction R.

By coiling the tube 20 in such a manner the exhaust E from the boiler cannot pass axially through the stack 12 a (or, at least it is very difficult for exhaust to pass through the stack 12 a in an axial direction) between the individual layers of tube 22 a-22 i. Thus, when multiple coil stacks 12 (e.g., adjacent stacks 12 a-12 b) are arranged axially relative to one another (e.g., stacks 12 a-12 b are spaced apart, axially, by a distance D₁), exhaust E is permitted to flow radially between the stacks, as shown in FIG. 3.

The efficiency of the overall economizer 10 depends on the relationship between heat transfer and a pressure drop of the exhaust E (e.g., exhaust pressure drop). Heat transfer, in this context, may be defined as the amount of heat allowed to transfer between the fluid within the economizer 10 (in particular, the fluid within the stacks 12) and the exhaust E. Efficiency of heat transfer is related to the heating surface available to the exhaust E. Exhaust pressure drop may be defined as the difference between the pressure of the exhaust E as it enters the economizer (e.g., at the exhaust flow conduit 18) and the pressure of the exhaust E as it exits the economizer (e.g., after passing radially between the stacks 12). Exhaust pressure drop may alternatively be defined as the pressure required to pass the exhaust E through the economizer.

As one would appreciate, there is a tradeoff between overall economizer efficiency, and the exhaust pressure drop. That is, decreasing the distance D₁ between stacks may lead to more efficient heat transfer, however this also leads to a large pressure drop, requiring more energy (e.g., in the form of a separate fan or blower required to draw the exhaust E through the economizer 10).

Included among the variables affecting the relationship between heat transfer and exhaust pressure drop are the axial gap D₁, stack size D₂ (or, overall stack diameter, represented in FIG. 2), tube diameter D₃ (represented in FIG. 4), and the number (or quantity) of stacks 12 selected for use therein.

As one example of the relationship between exhaust pressure drop and heat transfer, as the axial gap D₁ decreases, overall heat transfer increases, as does the required exhaust pressure drop. If the axial gap D₁ is too small, a separate blower or fan may be required to draw (or blow) the exhaust E through the economizer, increasing the energy required to operate the economizer 10. Further, the exhaust E may contain soot, which could potentially clog a small gap.

On the other hand, a large axial gap D₁ leads to reduced heat transfer between the exhaust E and the stacks 12. As mentioned, efficiency of heat transfer is also related to the heating surface available to the exhaust E. Thus, when D₁ is too large, fins may be included to compensate for the lack of heat transfer.

To optimize the relationship between heat transfer and exhaust pressure drop, the axial gap D₁ is related to tube diameter D₃ by a ratio within the range of 0.25:1 and 0.5:1, in one example.

In one example, the axial gap D₁ is within the range of about 0.1875 and 0.375 inches (between approximately 0.48 cm and 0.95 cm), the number of coil stacks selected for use is within the range of 30 and 36 coil stacks, and the tube diameter D₃ is about 0.75 inches (approximately 1.9 cm). As used herein, the terms “about,” approximately, and the like, should be construed to mean within dimensional tolerances accepted in this industry. Further, the stack size D₂ is then selected based on D₁ and D₃ to allow for a transfer of at least 10% of the heat from the exhaust E to the fluid within the economizer 10. These dimensions provide one example of an efficient tradeoff between heat transfer and exhaust pressure drop, however this disclosure is not limited to the above-mentioned dimensions, and variations thereof come within the scope of this disclosure.

In general, disclosed economizer 10 allows for efficient heat transfer between the exhaust E and the working fluid, which again may be water, carried within the stacks 12 while reducing the exhaust pressure drop required to effectively communicate the exhaust through the coil stacks 12. In the example that the working fluid is water, the disclosed arrangement takes advantage of water condensing on the outside of the coil stacks 12 to increase heat transfer. Namely, relatively cold water within the economizer 10 is heated by the exhaust E, and condenses on the outside of the coil stacks 12. This relatively cold water absorbs latent heat, allowing for absorption of the exhaust E. Further, and in general, the above-described configuration allows the economizer 10 to mainly recover latent heat, adding to the efficiency of the system (including the economizer 10 and the associated boiler).

The disclosed economizer 10 may be completely made of stainless steel. Other materials may be used, however, but stainless steel may have the advantages of being relatively inexpensive as well as providing for efficient heat transfer, and further being anti-corrosive.

The economizer may be contained in one of a plurality of economizer housings 24 a-24 c and may be arranged relative to a boiler 26, as shown across FIGS. 6-10. This disclosure is not limited to any particular use for the above-discussed economizer, and extends to all types of economizers.

The disclosed economizer is relatively compact and efficient. Further, in the disclosed example, no exhaust fan is required to communicate the exhaust from the boiler through the economizer 10, and no heat-transfer fins (e.g., fins used primarily to transfer heat between exhaust and the working fluid, rather than the fins T, which are used to swirl a fluid flow) are required to increase heat transfer. Accordingly, the disclosed economizer is relative low cost and low maintenance.

While water has been mentioned as a working fluid carried within the economizer 10, other fluids may be employed herein. Further, economizers used in other areas, such as those not associated with a boiler, may benefit from this disclosure. Thus, this disclosure is not limited to economizers that are associated with a boiler.

Although the different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples.

One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content. 

What is claimed is:
 1. An economizer comprising: a plurality of coil stacks, each coil stack including a tube coiled such that adjacent layers of the tube contact one another in a radial direction, the coil stacks axially spaced from one another to allow exhaust to flow between adjacent coil stacks.
 2. The economizer according to claim 1, wherein the coils stacks are axially spaced from one another such that an axial gap is provided between adjacent coil stacks, the axial gap related to the diameter of the tubes by a ratio within the range of 0.25:1 and 0.5:1.
 3. The economizer according to claim 2, wherein the axial gap is within the range of about 3/16 inches (0.48 cm) and ⅜ inches (0.95 cm).
 4. The economizer according to claim 3, wherein there are between 30 and 36 coil stacks.
 5. The economizer according to claim 4, wherein the tube diameter is about 0.75 inches (1.9 cm).
 6. The economizer according to claim 1, wherein the economizer does not include any heat-transfer fins.
 7. A heat recovery system comprising: a boiler configured to generate a flow of exhaust; and an economizer including a plurality of coil stacks, each coil stack including a tube coiled such that adjacent layers of the tube contact one another in a radial direction, the coil stacks axially spaced from one another to allow the exhaust from the boiler to flow between adjacent coil stacks.
 8. The system as recited in claim 7, wherein each coil stack is disposed about an axis, the economizer arranged relative to the boiler such that the exhaust enters the economizer flowing in a direction parallel to the axis.
 9. The system as recited in claim 8, wherein the exhaust flows radially, in a direction perpendicular to the axis, between adjacent coil stacks.
 10. The system as recited in claim 7, wherein a flow of a working fluid is provided to the economizer, the working fluid heated by the exhaust from the boiler.
 11. The system as recited in claim 10, wherein the working fluid is water.
 12. The system as recited in claim 10, wherein the economizer includes an inlet manifold in communication with each of the coils stacks, the working fluid provided to the inlet manifold.
 13. The system as recited in claim 7, including a conduit configured to direct exhaust toward the economizer, the conduit including a plurality of fins configured to swirl the flow of exhaust as the exhaust enters the economizer.
 14. The system according to claim 7, wherein the axial gap is within the range of about 3/16 inches (0.48 cm) and ⅜ inches (0.95 cm).
 15. The system according to claim 14, wherein there are between 30 and 36 coil stacks.
 16. The system according to claim 15, wherein the tube diameter is about 0.75 inches (1.9 cm).
 17. The system according to claim 7, wherein the exhaust flows from the boiler to the economizer without the aid of an exhaust fan.
 18. A method for heating a working fluid comprising: providing a boiler; providing an economizer including a plurality of coil stacks, each coil stack including a tube coiled such that adjacent layers of the tube contact one another in a radial direction, the coil stacks axially spaced from one another; establishing a flow of a working fluid within each of the coil stacks; and establishing a flow of exhaust from the boiler between adjacent coil stacks to heat the working fluid carried within the coil stacks.
 19. The method as recited in claim 18, wherein the working fluid is water.
 20. The method as recited in claim 19, including condensing water on the outside of the coil stacks to increase heat transfer between the exhaust and the water carried within the coil stacks. 